1. Field
Apparatuses and methods consistent with the exemplary embodiments relate to an image forming apparatus and a fixing unit control method thereof, and more particularly, to an image forming apparatus and a fixing unit control method thereof, which can prevent malfunction of a contactless sensor for sensing temperature of a fixing unit.
2. Description of the Related Art
An image forming apparatus forms an image to be printed on a printing medium. The image forming apparatus may be embodied in a printer, a copy machine, a facsimile, a peripheral having two or more functions, etc.
Specifically, an image forming apparatus 100, such as shown in FIG. 1, forms an image by an image forming unit which includes an image carrying body 121, an optical scanning unit 123 scanning a beam to the image carrying body 121 and forming an electrostatic latent image, a developing unit 125 for developing a toner image corresponding to the latent image formed on the image carrying body 121, and a transfer unit 130 transferring a toner developed on the image carrying body 121 charged with electricity to a printing medium.
An image transferred to the printing medium is thermally pressed by the fixing unit 140 and discharged to the outside. The fixing unit 140 is heated with supplied power and fixes the image on the printing medium.
The image forming apparatus 100 is provided with a temperature sensing unit (or a temperature sensor) that senses temperature of the fixing unit 140 in order to prevent the fixing unit 140 from overheating, and controls power supplied to the fixing unit 140 on the basis of sensing results.
In general, the temperature sensing unit employs a contact sensor contacting a heat roller 141 of the fixing unit 140 and sensing the temperature.
Also, the image forming apparatus is additionally provided with a contact-sensing protector that protects the fixing unit 140 by shutting off power supplied to the fixing unit 140, that is, turning off the fixing unit 140 regardless of a temperature control signal of a controller if the fixing unit 140 supplied with power is abnormally overheated due to a control error or the like reason or if an error occurs in the contact sensor.
However, in the case of the contact sensor, there may arise a problem that a contact part on the surface of the heat roller 141 is different in smoothness from the other parts, a sensed temperature is lower than an actual temperature since a pollutant such as a toner residue, a paper dust, etc. is attached to the contact sensor, and so on.
Recently, a contactless temperature sensor has been provided as an auxiliary means for the contact sensor, or there has appeared a tendency to control the temperature of the fixing unit 140 by using a contact temperature sensor as a sub temperature sensor in the periphery or the like of the fixing unit 140 and a contactless sensor as a main temperature sensor for the fixing unit 140 or by using only the contactless sensor.
A conventional image forming apparatus uses the contact-sensing protector for preventing the fixing unit 140 from overheating, an error, etc. on the basis of the sensing results of the contact sensor, but does not use a circuit for shutting off the power in hardware to prevent the fixing unit 140 from overheating, an error, etc. on the basis of the sensing results of the contactless sensor.
Also, the contact sensor includes a single sensor for sensing temperature, but the contactless sensor includes two sensors, i.e., a thermo-sensitive device for sensing infrared and a thermo-sensitive device for compensating temperature. Therefore, it is impossible to directly apply the contact-sensing protector to a contactless-sensing protector.
Accordingly, as demand for the contactless sensor increases, there is a need for separately providing the image forming apparatus with a contactless-sensing protector that protects the fixing unit 140 in hardware from abnormal overheating, an error due to malfunction of the controller, etc. on the basis of the sensing results of the contactless sensor.